Method of forming all ceramic denture



Aug. 25,; 1942. P. w. LEE ETAL. 3,999

METHOD OF FORMING ALL QERAMIC DEN'IURE Griginal F'ilejd May 31'. 1939 I5 Sheets-Sheet 1 Exmmemu ExpAuemu Iu FIG. 1 Pencean O com'ngq \ou omemm. LENGTH .ota

m5 NVESTMENT HATER-\AL Cmncm. Rmsr.

m Dsm'uqa BASE CERANK. Boov FREEZ\NG POINT OF PLATE Domum'u mangane- \00 200 500 400 500 600 '100 800 900 I000 00 \200 B00 \400 I500 I600 TEMPERATURE-"F IN VEN TOR.

DYUNGTOO WILLQAM LEE cumuzs 0| ATTORNEY.

Aug. 25, 1942. P. w. LEE ETAL 9 METHOD OF FORMING ALL CERAMIC DENTURE Original Filed May 31, 1939 5 She ets-Sheet 2 EXPANSION Ewgugnou 1N PERceN-r OF CONTRACTION I ORGHQAL LENGTH MATERIAL PLAsrER 5AND \00 206 300 400 500 600 100 800 900 I000 IIOO \EOOBOOMOOISOOIW TEMPERATURE- F INVENTIOR.

PYUNGTOO W\LL.|AM LEE BY CHARLES DIETZ TTORN Aug. 25, 1942. P. w. LEE ETAL 2,293,909

METHOD OF FORMING ALL CERAMIC DENTURE Original Filed May 51, 1939 3 Sheets-Sheet 3 PYUNGTOO WILUAM LEE y AND CHARLES T ATTORNEY.

Patented Aug. 25, 1942 Pynngtoo William Lee and Charles Diets, York,

Pa., as'signors to The Dentists Supply Company of New York, New York, N. Y., a corporation of New York Original application May 31, 1939, Serial No.

Divided and this application March 20, 1940, Serial No. 324,986 7 4 Claims.

This invention relates to an all ceramic denture, and has particular reference to the method of manufacturing such a denture wherein the teeth and denture base form an integral unit. 7

This application is a division of our co-pendin application filed May 31, 1939, Serial No. 276,644.

In the dental art, the molding or attaching of teeth of one ceramic body to another of different composition and at a temperature lower than the fusing temperature of the higher fusing body has not been successful up to date, v although the theory has been advanced and much claim has been made in dental literature and in patent specifications. Claims have been based on the assumption that two different bodies of like coefilcients of expansion and contraction could be made or developed, but in practice no'one heretofore has been able to produce two such different bodies of different compositions whose coeflicient's of.

expansion and contraction are alike, at least, through the critical range from atmospheric temperature to the plastic stage of the lower fusing material, and from that plastic temperature to atmospheric temperature.

It has been found in practice that if the difference in the linear expansion and contraction of 1 two ceramic bodies is greater than one-tenth of one per cent at any point between the plastic stage of the lower fusing body and room temperature, the two bodies cannot be attached or molded together without producing checks and cracks in either one or the other of the bodies.

The object, therefore, of the present invention is to provide a method whereby to produce an integral ceramic unit from two ceramic bodies having widely diverging fusing temperatures. I

A further object of the'invention is to provide a method of producing a denture having the teeth and base formed in an integral unit, in which the ceramic body of the teeth has a, higher fusing temperature, and theceramic body of the base has a relatively low fusing temperature.

A still further object of the invention is to pro- 7 vide a method for fusing into an integral unit two ceramic bodies, having widely different fusing temperatures, without resulting checks, cracks, etc;

The teeth may be made of ceramic body fusible at a substantiallyhigh temperature, and the denture base ceramic bodyfusible at relatively lower temperature. These ceramic bodies are then fused to form an integral unit in materialwhose thermal contraction through the critical range is in harmony with that ,of said teeth ceramic body and base ceramic body. g

The drawings illustrate an'exempliflcation of the method employed andthe views thereiniare as follows: a

. Figure 1 isa' graph sheet having'as abscissae degrees of temperature in Fahrenheit scale, and as ordinatesllinear expansion graded in=thbusandths of an inch, the thermal iexpansion of graduated in ten-thousandths of an inch. The

corresponding percentages of expansion are also given,

Figure 2 is a similar sheet and depicts the thermal expansion curves of two commercial investment materials of general use, ordinary feldspar;

the novel investment material, *and the novel tooth ceramic material,

Figure 3 is a plan view of a denture base model' invested in one half of an investment flask and 0 shows a temporary denture base with teeth attached applied to said model, I

Figure sis a cross-sectional view on the lines 4- of Figure 3, e

Figure 5 is a like view showing the other half of the flask applied and the temporary denture base with teeth invested therein, 4 v

Figure 6 is a similarview showing the flask invertedxand separated and the temporary denture base removed, f g I V Figure 7 is a like view showing the novel den ture base ceramic body residing in the space formerly occupied by the temporary denture base, and the flask parts re-united, and I v Figure 8 is a like view showing the relation of parts after fusion of the denturebase ceramic To accomplish all the objects hereinbefore set forth,vit is necessary to provide ceramic bodies and investmentmatcrial whose curves of expansion and contractionthrough certain ranges are.f'

harmonious. Nothing foun in the prior art will accomplish the results in or er to fulfill the foregoing objects.

After providing a ceramic body for the teeth with a suitable expansion and contraction curve,

mospheric temperature and the softening temperature thereof.

In Figure 1, the thermal expansion and contraction curve for the tooth ceramic body is shown by a full light line, and marked "Tooth ceramic body." The common and principal ingredients from which artificial porcelain teeth are usually produced are feldspar, kaolin and silica. Their proportions may differ.

' As a ceramic body for the artificial teeth giving the thermal expansion and contraction curve shown in Figure 1, we have devised a formula follows:

Per cent Feldspar 70 to 90 Amorphous silica.--" to 30 The teeth of this ceramic body may be manufactured either for general commercial use containing the usual-dental pins, either of base or precious metal, or may be provided with other means for fastening them to usual and ordinary denture bases. For the purpose of this invention, all such fastening devices may be eliminated, and we shall hereafter refer to teeth without any of these fastening devices as "bare teeth.

The denture base ceramic body of this invention is compounded in such a way that its thermal expansion and contraction are substantially harmonious with the thermal expansion and contraction of the porcelain of the teeth. This is especially so through the critical range which comprises from atmospheric temperature up to the fusing temperature of the denturebase ceramic body, or vice versa. It is especially important that the contraction, curve be in agreement from the softening point of the denture base material down through the hardening range to room temperature in order that no cracking may occur, and in order that a perfect union between the two ceramic bodies may be efiected.

The softening, maturing or fusing point of the denture base material may be considerably lower than the fusing point of the tooth material. In the present invention, the fusing point of the tooth material may be from approximately 2300' to 2400" F., while the fusing point of the denture base material may be from approximately 1500 to 1600' F. Consequently, the ceramic body of which the teeth are made may be termed a high fusing dental porcelain, while the ceramic body of which the denture plate or base is made is between porcelain and glass, probably being closer to glass than to porcelain. The denture base ceramic body which has been developed, and which produces a thermal expansion and contraction curve, such as that marked in Figure 1 of the drawings Denture base ceramic body, has the following formula:

Per cent Feldspar- 65 to 80 Amorphous silica 10 to Borax glass 5 to'15 In the ceramic bodies of both the tooth and denture base we have utilized amorphous silica for the following reasons:

1. It produces a low coefilcient of expansion and contraction:

2. Its substitution for regular silica lowers the maturing or fusing temperature of the bodies;

3. It eliminates the silica inversions, thereby producing a curve nearer to a straight line;

4. Because of its very fine particle size, it can be more easily and uniformly mixed in the bodies and lowers their fusing temperatures.

5. It produces stronger bodies.

Under proper control of temperature and time of firing, the tooth and denture base ceramic bodies of the foregoing formulae will expand and contract in substantial harmony. (See Fig. 1.)

In carrying out the process of forming our improved denture the teeth are molded and fired in the usual way. .A model I I), made from the novel investment material and exactly duplicating in size and form the. area to be covered by the denture base is cast, and this is invested in the 'novel investment material Ii in the usual manner in the lower half l2 of a flask. Suitable escapeways 9, as usually provided, may also be provided in carrying out this process. On this model III is a temporary denture base It composed of material which can be readily melted and which has the artificial teeth It set therein.

This temporary denture base [3 is identical in form with the permanent denture base to be procured. (See Figs. 3 and 4.) The upper hall of the flask then has a gasket it placed on its upstanding peripheral edge, and the lower half I! of the flask separated from the upper half by this gasket. Investment material 18, identical with the material H and with the material of the model ll), is then poured in through openings in the top of the upper half ll of the flask until the same is completely filled. (See Fig. 5.) After the investment material in the upper half has set or hardened so as to secure the artificial teeth therein the fiask may be inverted, boiled or heated, separated, and the temporary denture base melted or washed out. This also removes the material from the escapeways I. (See Fig. 6.) The gasket it, which formerly separated the halves of the fiask, is then removed and the novel ceramic body is of the denture base filled into the space f rmerly occupied by the temporary denture base I3. The halves of the fiask are then re-united. The flask is now ready for final processing to form the all ceramic denture by fusing the denture base ceramic body to the teeth.

In addition to the technical difilculty of developing a high fusing tooth ceramic body and a low fusing base ceramic body, which are in substantial harmony in expansion and contraction, certain practical advantages are obtained by having the denture base ceramic body fused around 700 to 800 F. lower than the tooth ceramic body. There is no danger of the vitrified teeth being deformed by a heat too close to their softening temperature. The temperature cited will not affect stains or other markings placed on the face' of the teeth to achieve certain artistic effects. The type of investment used to form the denture plates need not be excessively high fusing. Because this required temperature is comparatively low, the furnace for fusing the plate ceramic body to the teeth need not be intricate or expensive. The metal fiask, Just above described, in which the fusing is accomplished, may be made from this new investment material is as follows:

' Before placing investment material in either section of theflask, the side walls of the same have been lined with material 22 which will burn out, compress or otherwise allow for the expansion of the investment material, as shown and described in United States Letters Patent 2,228,059 issued to Pyun'gtoo William Lee,one of the applicants herein, on January 7, 1941.

pansion and contraction in practical agreement and harmony with the expansion and contraction of both the tooth ceramic body and denture base or plate ceramic body, in order that no checking or fracturing of the teeth or plate-shall occur in the cooling process.

Dental investment compositions generally con- *tain a considerable portion of quick setting material, such as gypsum or plaster of 'Paris, together with silicious materials, such as silica-sand and fire clay grog: V 1

In the drawings, Figurez shows a thermal expansion curve of an investment material having plaster of-Paris and 80% silica grog. That same figure shows another thermal expansion curve of an investment material having" plaster of Paris and 75% silica-sand. The thermal expansion curve of gypsum-silicamixtures, as shown, is generally characterized by certain sharp breaks due to silica inversions and to dehydration of the sulphate. It has been shown in Figure 1 that the thermal expansion and contraction curves of the new tooth ceramic body and of the new denture base ceramic body have been placed in the recess formerly occupied by the temporary denture base andthe flask sections re-united,'the flask is then placed in a kiln and the temperature gradually raised to the softening" temperature of the denture base ceramic body, whereupon pressure. is preferably added to the top of the flask to accelerate the coming together of the sectionsof the flask (see Figure 8) This may be accomplished by merely placing a weight of a few pounds on the upper flask section. It, of course, will be readily seen that the upper part of the flask will, by its weight or by gravity, come into contact with the lower part of the flask when the denture base ceramic body becomes soft, but the weight will hasten that step and allow for cutting off the heat to the kiln. By adding the weight or premix-e to the upper part of the flask, we, therefore, accomplish the following objects:

- 1. Economize in fuel: I '2. Savetime; t

3. Prevent the temperature from going beyond j the necessary temperature to soften the denture been brought into practical conformity, whereas the curves of the commercial investment materials, shown in Figure .2, are widely divergent from the curves of the tooth and base ceramic materials, the former of which is also shown in 1 Figure 2. A denture base formed in investments,

' curves of the tooth and denture base ceramic bodies hereinbefore described. The formula for Per cent A form of calcium sulphate (Hydrocal) 10 to 25 Feldspar Y 30 to 80 Silica grog 10 to 45 The thermal expansion and contraction curve of this investment material is shown in Figures '1 and 2.

curves of the tooth ceramic body, the denture base ceramic body and the investment material are always controlled so as to vary one from the base ceramic body.

Dentures made according to the foregoing description, and with the given formulae, have been produced over a period of time, and the process herein described has proven to be substantially one hundred percent perfect. Care has been taken to make no unjust claims, and to, be

ture base ceramic body and the investment material, and the fit and comfort of the resulting dentures, before the filing of an application for patent thereon.

The invention has many' advantages. Among these are- V (a) The teeth and denture base comprise an integral unitary structure;

(b) Bare teeth may be used without metal or any other form of anchorage;

(c) Partial plates may be made;

((1) The natural gum pink color of the denture plate is non-fading;.

(e) The denture plate is not subject to w'arpage or to change of form found in vulcanite plates and in synthetic resin plates;

(f) The denture itself will not permit infiltration of the acids of the mouth. It is, therefore, always clean, free from odors, etc.;

(0) Ceramic material denture bases are kind to theorai tissues and have a pleasantly cool feeling. The mat -flnish of this denture base ceramic body lends itself to a better adaption and fitting to the oral tissues;

' (h) Eliminates the danger of teeth dropping from the denture base as in other types of denture base.

Of course, the process of making all ceramic dentures may be modifled and changed in variintegral all-ceramic denture in a two-part flask, said method.comprising the steps of first forming from suitable investment material a dental model, then placing thereon a temporary denture base having teeth fusible at substantially high temperature, then investing said model and temporary denture in one part of the flask, then combining the flask parts and supplying investrnent material to the other flask part to invest the teeth therein, then separating the flask parts, then removing said temporary denture base by applying heat, then inserting in the resulting 'cavityof the flask part containing the teeth a predetermined quantity of denture base ceramic material sufllcient to initially maintain the flask parts slightly spaced when assembled and having a fusing temperature substantially lower than that Jot said teeth, then applying the other flask part whereby the assembled flask parts ,will be disposed in slightly. spaced relation, and .then applying heat and pressure until the flask parts meet and the base and teeth are fused into an 'integralunit, 7 2. The herein described method of formingan integral all-ceramic denture in a two-part flask, said method comprising the steps of flrst forming from suitable investment material. adental model, then placing thereon a temporary denture base having teeth fusible at substantially high temperature, then investing said model and temporary denture in one part of the flask, then combining theflask parts and supplyinginvestment material to the other flask parttoinvest the teeth therein, then separating the flask parts, .then removing said temporaryv denturebase by applying heat, then i'nsertingin, the resulting cavity of the flask part containingethe teeth a predetermined quantity of denture base ceramic material sufllcient to initially maintain the flaskparts slightly spaced when assembled and having a fusing temperature substantially lower. than that of said. teeth, then applying the otherflask part, wherebythe assembled flask parts will be disposed in slightly spaced relation, and then heatingthe assembled flask parts to the fusing temperature of the denture base ceramic material and applyingpressure to close the flask and fuse the base and teeth into an integral unit.

3. The herein described method of forming an integral all-ceramic denture in a two-part flask, said method comprising the steps of first, forming from suitable investment ,amaterial a dental model, then placing thereon a temporary den- .ture base havingiteeth fusible at substantially high temperature, then investing said model and temporary denture in; one part oi the flask, then combining the flask parts-and supplying investment material to the other'flask part to invest the teeth therein, thenseparating the flask parts, then removing said temporary denture base by applying heat, then inserting, in thevresulting cavity of the flaskpart containing the teeth a bled and having a fusingtemperature substan-' predetermined quantity oft, granular denture baseceramic material sumcient to initially maintain the flask parts slightly spacedwhen assem- ,viding a, two-part flask @fOI' forming a denture,

. one part of said flask containing pre-flred porcelain teeth with a timing temperature higher than that of the ceramic denture base material, inserting, in the flask part containing the teeth a predetermined weight of ceramic denture base ,material sufllcient to initially maintain the flask 

